99Z15 BACK_ROUND OF THE INVI:NTION 2 ( 1) Fie ld of the Invention . 3 The present invention relates to novel electro- 4 chemical cells having electrolyte compositions containing S specified compounds. More speci~ically, the present inven- 6 tion is directed to rechargeable, high energy den~ity 7 electrochemical cells having alkali metal anode~, chalco~ 8 genide cathodes and containing electrolyte compositio~s 9 consisting essentially of solvent and electrolytically lo active alkali metal salts including a polyaryl metallic 11 alkali metal salt. ; 12 (~ Prior Art 13 A recently developed rechargeable~ high energy 4 density electrochemical cell consists of an alkali metal material as the anode ac~ive m~terial, a transition metal 16 chalcogenide as the cathode-active material, and a non- 17 aqueous electrolyte. More specifically, preferred cells 18 consist of lithium anodes, titanium disulfide cathodes and 19 nonaqueous electrolyte compositions consisting of various ~ lithium sal~s9 such as LiC104, dissolved in organlc solvents, 21 such as propylene carbonate, tetrahydrofuran, dioxolane, 22 and mixtures o dimethyoxyethane and ~etrahydro~uran, and ~3 containing various stabiliæing additives. 24 Tmportant ~eatures of these cells include their ability to be repeatedly discharged and charged~ Theoreti~ 26 cally, cycling by discharging and oharging should be possible ,: . 27 inde~initely, but in practice indefinite cycling is not ~: 2~ xealized . Dendritic grow~h on ~he anode during charging ~ and degradation of the cathode material are sometimes ~- l~miting ~actors in the amount of cycling to which a cell 31 can be subjected. Howe~er? the electrolyte, part-i.cularly 32 nonaqueous electrolyte~, can at times be the limiting factor. . ~ -- 2 - . . g~ l Ths effec~s of a par~icular elee~xoly~e c~mposi~on on the 2 electrochemical performance of a cell may be sign~ficant 3 due to its relative stability or it may be due to other 4 factors~ One particular electrolyte con~osition might be highly effective with a given anode-ca~ho~e couple but be 6 ine~fective for another coupleg either because it is not 7 ~nert to the second ouple or because it rea~s with ~tself 8 under the conditions present during cycl~ng. Furthermore, 9 even when a particular electrolyte composi~ion is efective ~lO ln a given cell, it may nontheless be undesira~le for : 11 other reasons~ For example5 tha sometimes preferred LiC104 . 12 based electrolyte creates a potential e~plos~on haæard. l3 And, ~or example~ various organome~allic alkal~ me~al salt 14 compounds such as are described in U~S~ Patent Nos. 3,734~963 and 39764,385 have the disadvantage of requ~ring 16 complexing with various n~trogen, phosphorus or sulfur- 17 containin~ organic compounds containing at least two func~ ~: l8 tionalities~ 19 A study has been made directed to LiB(C6~ls)~ electrolyte systems by Bhattacharyya, Lee, Smid and Swarc, ~l J Phys. Chem.~ Vol~ 69l p~ 608 et seq~ ~196S) but no 22 sugge9tion is made therein that such systems may be used 23 ~n cells conta~ning alkali metal anodes~ Also~ ~he i 24 Bhattacharyya et al systems`have been fou~d to have low 2s solubility and high resistivity~ United States Patent No, 26 3,935,025 describes anolytes and ca~hoLytes or sodium- 27 conta~ning batteries which contain specified alkali metal 28 salts~ e~g. NaB(C6Hs)4, ~n or~a~ic:solvents, but the refer~ ence fails to suggest the use o such systems having ~lkali metal anodes in combination with chalcogenlde cathodes. u.s. ~-~ 31 Patent No. 4~060,674, entitled "Alkali Metal Anode- 32 Contalnin~ Cells ~ 3 - ~L~ ~3~ Z ~ 1 Having Electrolytes of Organometallic Alkali Metal Salts and 2 Organic Solvents", ~sued on November 29,-1977 t~ the present 3 inventors, described various organome~allic alkali metal 4 salt electrolytes, e.g. LiB(CH3)4 and LiB(C6H5)3CH3, and c~lls containing these, the salts being limited to those 6 wherein at least one organic substituent is an alkyl radical. 7 It has I~OW been unexpectedly discovered that the salts used 8 as elec~rolytes in the present invention having all aryl ~- 9 radicals as substituents exhibit superior gassing inhibition and have been found to be excep~ional electrolytes fo~ alka~ ll metal anode/chalcogenide cathode cells in which gassing would ` 12 o~herwise be a problem. In fact, some of the pre~erred 13 electrolytes of the abovewmentioned copending application 1~ appeared to exhibit gassing which is typical of such elec~ trolytes, whereas at least some of the electrolytes used in 16 the present invention surprîsingly appear to exhibit sub~ - 17 stantially negligible gassing~ 18 DETAlLED DESCRIPTION OF THE INVENTION l9 The presen~ invention is directed to improved electrochemical cells having alkali metal anodes and ~l chalcogenide cathodes, and con~aining speci~ied electrolyte 22 compositi~ns. The electrolyte compositions consist essen- 23 ~ially of organic solvent and eleet~olytically active alkali 24 metal salts including a polyaryl metallic alkali metal sai.t of the formula: 1 26 2MRn (13 27 wherein Z is an alkali metal9 M is a metal selected ~rom ~he 28 group consisting o~ Zn, Cd, B, Al, Ga, In, Tl, Sn (stannous) ., P and As, R represents aryl radicals, as more specifically set orth below, and h is the number o organic radicals, 3l i.e., n is a numerical value equal to one plu5 the valence 32 of the metal M. . - 4 - ~9 9 Z8 ' l The alkali metal ~epresented by Z in Formula (1) ¦ 2 above is any alkali metal, but is desirably selected from 3 lithium, sodium and potassium, with lithium being the pre- `I 4 ferred embodiment ~ 5 The metal M in Formula (1) is any of zinc, cadmium, i 6 boron, aluminum, gallium, indium, thalllum, tin ~stannous), 7 phosphorus and arsenic. Desirably, M is selected ~rom the 8 group consisting of boron, aluminum, phosphorus and arsenic. 9 Most prefe~red is boron. j lO The aryl radicals represented by each R may be the ll same or different and are ine~tly s~bstituted or unsubsti- l l2 tuted aryl radic31s~ By "iner~ly substituted" is meant ¦ 13 radicals containing substituents which have no detrimental :` : -!i 14 e~ect on the electrolytic properties of the electrolyte lS comp~sition in ~he context of its e~fec~iveness in electro- ~, 16 chemical cells. These aryl radicals R may be, ~here~ore, ~L 17 inertly sub~ uted or unsubs~ituted aryl and include alkaryl r~dic~ls. Also, the compounds used in the present 19 invention include those o~ the above Formula (1~ in which ii 20 two of the ~. radicals may be bonded to one ano~her~ 21 general~ the compounds may be selected rom the group con~ 22 sisting of aryl radicals having 6 to S0 carbon a~oms 23 ~including alkaryl radicals having 7 to 50 carbon atoms). ~,~ 24 Desirable aryl radicals are the phenyl ~olyl, biph~nyl and r ~ 25 ~naphthyl radicals~ Preferred are the phenyl radicals. 26 ~Particularly use~ul are the salts wherein all of the organlc 27 ~ radicals are phenyl radicalsr~ ~t~ 28~ The variable n in~Formula (l) represents the 29 ~ number o~ organic radicals R and isg therefore, a numerical 30~ value equal to one plus the valence of the metal M. Thus, 31 n - 3 when M i.5 Zn~ Cd, and Sn9 n - 4 when M is B, Al, Ga, : 32: ~ ~ In~ and Tl, and n r~ 6 when M is P and As. ,., 5 ~ ~ 9~ 2 1 Exemplary polyaryl metallic alkali metal compcunds 2 which are desirable electrolytes for the electrochemlcal : 3 cells of the present invention include the ollowing: 4 ZM (C6H4)4 (2) : Z+ ~ \ M ~ 1 (3) 6 3 3 . 7 Z+ . M (~) ~ , . 9 ~ ~ CH3 ~ . CH3 . 11 whe~ein the variables Z and M are a9 defined above, and ~`` 12 e~pecially wherein æ i~ lithium and M ls boron. 13 The polyaryl me~allic alkali metal salts employed 14 in the present inventlon ~y be prepared by reacting mono- aryl alkal~ metal compounds w~t~ polyarylmetalLic compounds 16 in an organic solvent.~ This reaction is believed to be 17 represerited by the following equationo 18 ZR ~ MRn~l ~ Z lMRn] (a) 19 wherein the vari~blesa~e as defined for Formula ~1) above. : ' ;.: .' ' ~, ~(;?8~Z8 ~ ` The reaction may be carried over wide ranges of operable ~ 2 pressures and temperatures, and room temperature and pressuxe ~' 3 conditions will allow the reaction to readily occur in most 4 instances As mentioned9 the elec~rolyte composition employed 6 in the cell o the present invention consists essentially o~ 7 org~nic soLvent and electrolytically a~tive alkali me~al 8 salts including a polyaryl metallic alkall metal salt of 9 Formula (l) above. Thus, a mixture of salts is contemplated, at least one of which is a Formula (l) ~ype salt. The other 11 salt or salts in the mixture may be any electroly~ically ''' 1~ active alkali metal salt which is compatible wi~h the 13 Formula (l) type s~lt9 e.g. 9 LiBr9 LiI and the l~ke. Also 14 contemplated is the electrolyte which contains only one or 15 more salts of Formula ~1). Thus, the expression ~electro- 16 lytically active alkali metal Sal~9 including a polyaryl 17 metallic alkali me~al salt" should be construed to include: 18 (l) mixtures of polyaryl metallio alkali metal salt~s) and 19 other compatible alkali metal salts(s), and (2) one or more polya~yl me~allic salts wi~hout other sal~s. 'Pre~erred i9 21 the electrolyte containing the polyaryl metallic salt(s) 22 without other salts~ ` 23 Theo~n~ solven~ employed in the electroylte 24 composition employed in the ce'll o~ the present invention is generally one selec~ed from the group consisting of lnertly 26 substituted and unsubstituted ethers, esters, sulfone~, 27 organic sulfitesg organic sulfates, organic nitriteæ and ~ '` .~ 28 organic nitro compounds. By "~nertly substituted" solvent i8 meant one which contains subs~ituents which have no 30 detrimental efect ~on the electrolytic properties oE the i : ~ .. . : . 31 electrolyte composition in the context of ~ts effectivel1ess 3~ in electrochemical cells. These solvents may bq any of the ' ' ~ ,, - 7 - :: . . . ~ 2 8 1 foregoing which will function as either a diluen~ or as a 2 complexing solvent with the polyaryl metallic alkall metal 3 salt and which will~ with the salt, produce an effectiv~ ! 4 electrolyte. Thus, the solvents which are included are those composed of one or more compounds selected from : 6 straight chain ethers, polyethers, and cyclical ethers; 7 including such e~hers as the acetals, ketals and ortho- 8 esters9 and org~nic esters~ sulfones~ organic nitro compounds 9 and organic nitrites and org~nic sulfates snd sul~ites. Examples include propylene carbonate, tetrahydrofuran, 11 dioxolane, furan, sulfolanej dimethyl sulfite, nitrobenzene, 12 nit~o~meth~ne and the like~ The preferred solvents are the 13 ethers. For example, dioxolane, dimethyoxyethane, and . .: 14 mixtures of these are u~eulO Preferred is a solvent con- .. ~aining dioxolaneO .. 16 In general~ sufficient organic solvent must be 17 utiliæed to effe~ti~eLy render the polyaryl metallic alkali . 18 metal salt electrolytically ao~ive (io~o ~ adequately con- 19 ductiv~) when employe~ in an electroly~ic cell. The 80lvent: may be a mlxture of compounds as suggested above, and may 21 contain known electrolyts additives which are compatible 22 with the ~olvent and the paEticular salt employed. A~ to 23 the ~mount o~ salt to be employed in the organic solvent, 24 this will vary tremendously with ~he specific solvent usedS the salt chosen and the type of electrochemical cell per- 26 formance which is desired. In any event~ an electrolytica~y 27 active amount o~ salt must be added to ~he solven~. Typica~Lx 28 at least about Ool moles of salt up to sa~ration may be , 29 used per li~er of solvent9 e.g. 9 about O.l to about S moles/ ~. liter may be used and pre~erably about 0.5 to about 3 moles/ .~ 31 liter may be used. 32 The present in~ention rel~tes, in general, to 8 ~: ~ ~9~ ~ 1 improved high energy density electrochemical cells having2 alkali metal anodes, metal chalcogenide cathodes and electro- . 3 lyte compositions as described aboveO Th~s9 these cells 4 ~nclude those containing as anode-active materials any one S or more of the alkali metals, and alloys thereof Alkali 6 metals desirably used in the anodes are lithlum, sodium and 7 potassium, and alloys thereof~ Of these, lithium and lithium 8 alloys are preferred. 9 The present invention contemplates any cell having lo an alkali metal anode~ a metal chalcogenide ca~hode and an 11 electrolyte as defined above~ The cathode~actlve mater~al 12 may be any metal chalcogenide whlch is cathodically active 13 ~n alkali metal anode cells~ Among these, preferred are the 14 transitlon metal chalcogenide cathode-~ctive materials, includ~ng those.containing at least one member selected from 16 the group consist~ng of molybdenum~ t-ltanium, zirco~ium, haf- 17 nium, niobium~ tantalum and vanad~um~ and a~ least one chal- 18 cogen selec~ed ~rom oxygen, sulur, selenium~ and tellur~umO 19 Of the chalcogenides me~tioned~ most advantageous are the sul~de~0 0~ the transition metal chalcogenides, pre~erred 21 are the dichalcogenides, and the most preferred is t~tanium 22 d~sul~ide~ 23 The ~ollowlng examples are presented as merely 24 being illustra~ve o the present invention, and the ln- 2s vention should not be construed to be limited there~ 26. ~o, 27 EXAUPLE 1 ~ : 23~ LiB(~6Hs)4 ~ (dloxolane)3,3 ~: : To a 350 ml~ flask filled wlth an N2 inlet and : ~ contain~ng a ma~netic stlrrer bar ~s charged 34022 g (0~1 31 mole3 o~ NaB~CGHs)~ and 75 ml o~ dry dioxola~e, Wlth . . . : _ g _ ~' ~ 9 ~ ~ ~ 1 stirring~ 16096 g ~004 mole~ of lithium chloride in 75 ml 2 . of dioxol~ne is added and this mixture ls maintained at 50 3 60C. ~or about two hours then at room temperature ovarni~lt. 4 The solids are removed by centrifugation and the clear supernatant solu~ion is evaporated to give 55.6 g of white 6 solid. This is dis~olved, under an atmosphere of dry N2, in 7 the minimum amo~nt of warm e~hylenedichloride, then an equal 8 volume of heptane i8 added to precipitste the salt. The 9 latter is collected by filtration to afford 46.3 g of re~ 10 cryst~llized saltO A 0.352 g sample of this material, : 11 dissolved in 00328 g of dimethoxyethane, i5 used to obtain 12 a pro~on nmr speet~wmO ~he spectrum shows multiplets at 13 7054 and 7015 ppm for the B~C6H5)4 anion (20 H) and sin- 14 glets at 4.90 and 3078 for dioxolane (20 H) to establish a composition LiB(C6H5~ ~ (dioxolane)3 3 for the salt. 16 ~lemental ~nalysis~ calcO for LiB(C6Hs)~ o (C3H602)3,3 l7 C 71. 35~L, H 7 o 03%, Li 1.22% `: 18 Found: C 71-26~/D H 6.90%3 Li 1.22%, Na~ 0.005%~ Cl 0.21%. I9 A satura~ed sclution of LiB~C6H~)~t iS prepared in dioxolane. Nmr analysi~ of this solution shows the salt concentration 21 to be 0097 moles/~iter dioxolaneO Dllutions are made ~rom 22 this stoek soluticn and A~Co rasistivities are measured as . 23 a ~unction o solute eoneentration~ molality ~ohm cm): .. . 24 0078t225) 9 0~52(255~, 0036(3~9) ~ and 0.27(408) . : ~5 EXAMPL~ 26 By the method of Example 1, the composition 27 LiB(C6Hs)4 (Te~rahydrofuran)306 is prepared in THF solvent. ~: 28 A~sample of loO99 g O~ this m~terial is dissolved ~n 0.311 g 29 of dimethoxyethane and 3 t 65 g of dioxolane . This solution, containing about 1. 0 8 Mole LiB (C6Hs) 4 in 4 0 3 ml o solvent : 31 whose composition ls 79% dioxolane~ 13% tetrahydrouran, and 32 8% dime~hoxyethane based on volume ~ 9hows a specific ;: ~ 10~ , ` . l . 1 resis~ivi~y of 265 ohm cm- 2 ~XAMPLES 3 T0 6 3 Gassing tests are perform~d as follows: 4 A weighed quantity of TiS2 is placed in a vial along with an aliquot of the elec~rolyte solution to be 6 tested. A glass U-tube having an extended bulbous sect~on 7 on one side contains mercury ~o a predetermined level in the 8 bulbous section so as to fill the non-bulbous section to 9 the brim. The vial containing the TiS2 and the electrolyte lo solution is placed inside the bulbous section of the U-tube 11 above the mercury. A greased cap is placed over the bul~ous 12 section to enclose the vialD The entire apparatus is then 13 placed in a constant temperature oven at abou~ 34C. The 14 amount of ga~ generated is measurad by collecting the mercury overflowing from the U~tube (which is displaced by the gas 16 p~oduced) and weighing the collected mercury. 17 Exsmplas 3 to 5 involve the testing of U.S. 18 Patent No. 4,060,674 (cited above) electrolytes 19 and Ex~mple 6 involves the te~ting o~ an electroly~e of the ~ 20 presen~ inven~ion. ; 21 EXAMPLE 3 22 Abou~ 10 cc o a 2.5 m LiB(CH3)~-DME ~glyme) 23 801utlon in dioxolane is plac~d in ~he test vlal in contact 24 with 3.0 gram~ o~ TiS2 and evolved gas is meas~lr~d ln the above descr~bed apparatus and anaLyzed. 26 EXAM}LE 4 27 About 10 cc of a 2.5 m LiB(CH3)4-diglyme soLution 28 ln dioxolane is placed in the test vial with about 3.0 gram~ 29 of TiS2 and tested as in Example 3. ~ EXAMPLE S 31 About 10 cc of a 2.5 m solution o~ LLB(CH3)4- 32 blglyme in dioxolane is placed in the test vial with 3.0 3~ 2 1 grams of TiS2 and tes~ed as in Example 3. 2 XAMPLE 6 : : 3 About 15 cc of a 1~6 m solution of LlB(C6Hs)4 ln 4 a 70:30 mixture of dioxolane: DME (glyme) is p1aced in the test vial with about 1.5 grams of TlS2 and tested as in 6 Example 3c 7 The test results for Examples 3 to 6 are shown in 8 Table I below. Most significan~ is the act that the : : 9 Example 6 solutlon shows no gassing a~ter 6 weeks of testing~ T~BLE I 11 ~U~ '`' `'''`' 12 Gas 13 ~ Gassin~ Analysis 14 3 (copending case~ lo9 cc/hr/g TiS2 Ethane, lS methane~ 16 and 17 B(C~I3) 3 18 4 (copending case) 0013 cc¦hr/g TiS2 Ethane9 19 methane, and :: 21 ~ B(CH333 22 5 (copending case) 00087 cc/hr/g TiS2 Ethane~ : 23 methane, 24 ~nd ` : . 2s B(CH ~ : 27 6 ~present ~nventi~n~ 00000 cc/hr/g TlS2 No gases 28 ~yyy~ a-~ 29 ~ddlt~onal gass~ t~ts are per~ormed using two 30 c~p~ndlng applica~ion eLectrolytes, L~B(C6H4-0-CH3)3CH3 and 31 LiB~C6Hs)3CH3~ ~or Examples 7 and 8, respectively, and 32 present inve~on electrolyte LiB(C6Hs)4 for Example 9. . . 33 The Example 7 and 8 systems are tested with 10 cc o~ electro~ , ... 34 lyte at 2~0 molallty in dioxolane, wi~h 0~75 grams of TiS2 : 35 cathode and the Ex~mple 9 system is tested with 15 cc of ; ;;~ 36 1c6 molali~y ln d~oxolane~ with 1~5 grams o~ TiS2 cathode ; 37 mater~al, ~n accordance with the pro~edure outIined above ; ` 38 for ~amples 3 to 6~ : ~ . - 12 - . . . 9 ~ 1 For the ~irst eight hours of testing~ significant 2 gassing is observed with ~he test cells of Examples 7 an~ 8, 3 followed by n.o gassing thereafter. During the en~ire period 4 of testing, no gassing whatsoever is observed with ~he present inventlon test cell of Example 90 6 EXAMPLE 10 7 A number of test cells are prepared with a lithium 8 anode, a TiS2 cathode and a lithium tetraphenyl boride- 9 dioxolane solution electrolyte~ To ~llustrate performance~ one eell having a 1~6 m LiB(C6H5)4-70~30, d~oxolane:DME ll electrolyte with a cathode loading to 13~8 mg-hss/cm3 ha3 12 a prlmary discharge of 94% MU and a discharge rate of 0.34 l3 ma/cm2 over 26 cycle~. '' ; '.' . . . ~'' .' ~~~7~7 ~ ~"~ 5~ r~